1. Field of the Invention
The present invention relates to a "spin-valve type" thin film element, in which the electric resistance varies as a function between the magnetization orientation of a pinned magnetic layer and that of a free magnetic layer, which is free to rotate with an applied magnetic field. The invention further relates to improvement of a magnetic material used as the aforementioned pinned magnetic layer.
2. Description of the Related Art
A spin-valve type thin film element is a kind of giant magnetoresistive (GMR) elements utilizing the giant magnetoresistance effect for detecting a recording magnetic field recorded in a recording medium such as a hard disk.
Such a spin-valve type thin film element is composed of at least four layers, i.e., a free magnetic layer, a nonmagnetic electrically conductive layer, a pinned magnetic layer and an antiferromagnetic layer laminated in this order on a suitable substrate, and pairs of a hard magnetic bias layer and an electric conductive layer are laminated on both sides of the four layers.
In general, the conventional spin-valve type thin film element comprises the antiferromagnetic layer composed of an FeMn (iron-manganese) alloy film or a NiMn (nickel-manganese) alloy film, the pinned magnetic layer and free magnetic layer each composed of a NiFe (nickel-iron) alloy film, the nonmagnetic electrically conductive layer composed of a Cu (copper) film, and the hard magnetic bias layer composed of a Co--Pt (cobalt-platinum) alloy film.
The pinned magnetic layer is formed adjacent to the antiferromagnetic layer. The magnetization of the pinned magnetic layer is put into a single domain state in a height direction (the direction of a leakage magnetic filed leaked from a recording medium) and fixed by forming the pinned magnetic layer in a magnetic filed when the antiferromagnetic layer is composed of an FeMn alloy film, or by annealing it when the antiferromagnetic layer is composed of a NiMn alloy film.
The magnetization orientation of the free magnetic layer is aligned with a track width direction by a bias magnetic field from the hard magnetic bias layer, and the magnetization orientations of the free magnetic layer and the pinned magnetic layer are at an angle of 90.degree. with respect to each other.
In a spin-valve type thin film element, a sensing current is fed from the electric conductive layer to the pinned magnetic layer, nonmagnetic electrically conductive layer and free magnetic layer. When a leakage magnetic field is applied from a recording medium to the element, the magnetization orientation (magnetization direction) of the free magnetic layer rotates from the track width direction to the leakage magnetic field direction (height direction). The electric resistance changes as a function between the variation of the magnetization orientation in the free magnetic layer and the fixed magnetization orientation of the pinned magnetic layer, and consequently the voltage changes according to variation of the electric resistance so as to detect the leakage magnetic filed from the recording medium.
Meanwhile, a large exchange anisotropic magnetic field generated in a boundary face between the pinned magnetic layer and the antiferromagnetic layer is preferred. This is because such a large exchange anisotropic magnetic field can satisfactorily put and fix the magnetization of the pinned magnetic layer into a single domain state in a height direction (leakage magnetic field direction from a recording medium).
To provide a large exchange anisotropic magnetic filed, various inventions and publications have been made in which materials of the antiferromagnetic layer and/or pinned magnetic layer are changed or conditions of a heat treatment to generate an exchange anisotropic magnetic filed are suitably adjusted.
It is, however, not only an exchange anisotropic magnetic filed that affects the magnitude of the magnetization. A magnetic filed generated by a magnetoelastic effect also affects the magnitude of the magnetization of pinned magnetic layer. Such a magnetic filed can be determined by a stress and magnetostriction applied to the pinned magnetic layer.
A spin-valve type thin film element has upper, bottom and height side surfaces covered with an insulation film (gap film) composed of, for example, Al.sub.2 O.sub.3, and an opposite surface to the height side (i.e., an Air Bearing surface (ABS) side; front surface) exposed to the outside. Since the spin-valve type thin film element is composed of a multilayered structure comprising metal films, its coefficient of thermal expansion is larger than that of the insulation film covering the element. Accordingly, a tensile stress directed to the height direction acts upon the spin-valve type thin film element.
When the pinned magnetic layer constituting the spin-valve type thin film element has a negative magnetostriction under the above mentioned condition, the magnetization of the pinned magnetic layer is induced in the track width direction by the magnetoelastic effect.
To be more specific, even if a large exchange anisotropic magnetic filed can be obtained which can satisfactorily put the magnetization of the pinned magnetic layer into a single domain state in the height direction, when a magnetic filed as a function of the magnetoelastic effect acts for orienting the magnetization of the pinned magnetic layer in the track width direction, the magnetization of the pinned magnetic layer is not rigidly fixed in the height direction. Therefore, reproducing characteristics are deteriorated, including an increasing incidence of Barkhausen noises.